Temperature plays an important role in the performance of batteries. Batteries are a function of chemical reactions. In cold weather, the chemicals cannot react as fast as in warm weather. A cold battery will, thus, not have the same power as a warm one. In order to provide sufficient electrical power in all weather conditions, it is thus sometimes necessary to increase the number of batteries or use bigger batteries. However, this results in weight increase, which makes hybrid electric power plants less attractive for aircraft applications.